MEANS OF COMMUNICATION. 35 
branch of the Dublin road to Dalkey was full of curves and inclinations 
which rendered the use of a locomotive perfectly impracticable; it was 
opened in December, 1843, and still continues in operation. 
In pl. 6, we have represented the Kingstown and Dalkey Railroad, and 
shall explain its construction sufficiently in detail to manifest the principle 
upon which it acts. In the centre of the track is laid a hollow cast-iron 
cylinder, which is secured to the sleeper by bolts and screws (jigs. 2 and 
4). The joints of the cylinder, where the separate pieces come together, are 
made air-tight, and are firmly secured by screws. Within the cylinder, 
which is 15 inches in diameter, moves a solid piston, B (figs. 3 and 4), with 
an exceedingly elastic packing, that it may adapt itself as nearly as possible 
to the small inequalities of the interior of the cylinder. The piston is pro- 
vided with an advancing head, which serves to open the valves, and has 
attached to it a piston-rod 18 feet long, the central portion of which is a 
plate, c, balanced by the weight, w, so that the piston always lies 
horizontal. 
The plate e has four rollers, © (jigs. 3 and 4), the object of which we 
shall learn hereafter. The driving-piston is connected to the carriage above 
by the plate p (jigs. 3, 4, 5, and 6), which, however, must pass through the 
cylinder, which has a slit running its whole length for the purpose. This it 
is necessary should be closed air-tight in advance of the piston, and open 
only at the moment of the passage of the plate p, that the pressure of the 
air may operate upon the back of the piston. /%g. 8 shows the arrange- 
ment adopted for this purpose. a is the cylinder, x1 the valve, which con- 
sists of a strip of stout sole leather covered with a thin plate of steel, sur- 
mounted by a cast-iron plate, x, which prevents the valve from being forced 
into the opening by the pressure of the atmosphere ; beneath the valve there 
is also an iron plate, not shaded in jig. 8, but seen in jig. 6, which entirely 
closes the opening in the tube; this latter plate is curved upon the same 
radius as the cylinder, that the piston may fit air-tight all round. At 7 
the leather valve is held firmly, and at 1 is a trough into which a composi- 
tion of wax and tallow is poured, which assists to pack the valve air-tight. 
In order to protect this apparatus from the weather, plates of sheet-iron, g, 
5 feet long and hinged at A, are made to hang over the whole. To under- 
stand the operation of this apparatus, we must turn to jigs. 3,5, and 6. The 
roller, H, upon the piston projects into the longitudinal slit, and raises the 
valve, K, breaking the wax cement which holds it to the cylinder; at the 
same time the roller, m, upon the bottom of the driving-car (figs. 5 and 6) 
comes under the plates, H, and raises them, so that the atmosphere is free 
to press upon the after-surface of the piston, which is thus driven along the 
cylinder, and with it the driving car, the two being connected together by 
the plate, p, as seen in jigs. 1 and 5. That the valve may be returned to its 
place after the passage of the plate, p, the driving-car carries a roller, F, 
( figs. 3 and 7), which runs upon the surface of the plate, x, and presses the 
leather, L, again down upon the valve-seat. At the same time, immediately 
over the trough, L, there passes a tube, eg, heated by a small furnace upon 
the driving-car, which melts the mixture of wax and tallow, and again packs 
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